Absence of germinal granules from germ plasm at fertilization does not affect the number of primordial germ cells that reach the genital ridges in tadpoles

1989 ◽  
Vol 27 ◽  
pp. 123
Author(s):  
K.E. Dixon
Keyword(s):  
Germ Cells ◽  
Germ Plasm ◽  
Primordial Germ Cells ◽  
Germinal Granules

Partial characterization of ‘primordial germ cell-forming activity’ localized in vegetal pole cytoplasm in anuran eggs

Development ◽  
1977 ◽  
Vol 39 (1) ◽  
pp. 221-233
Author(s):  
Masami Wakahara
Keyword(s):  
Germ Cells ◽  
Germ Plasm ◽  
Primordial Germ Cells ◽  
Primordial Germ Cell ◽  
Differential Centrifugation ◽  
Rana Chensinensis ◽  
Crude Homogenate ◽  
Germinal Granules ◽  
Vegetal Pole

Larvae of Rana chensinensis developed from fertilized eggs which had been subjected to ultraviolet (u.v.) irradiation on their vegetal hemisphere at a dose of 20000 ergs/mm2 within 60 min of fertilization contained no primordial germ cells (PGCs) when examined histologically at the stage when the operculum was complete (8 days after fertilization at 18 °C, stage 25 according to Shumway, 1940). The morphogenetic ability of vegetal pole cytoplasm from non-irradiated eggs to establish the PGCs was tested by injecting some fractions of this cytoplasm into the vegetal hemisphere of u.v.-irradiated eggs. Crude homogenate of the vegetal pole cytoplasm without large yolk platelets was able to restore the PGCs when injected into u.v.-irradiated eggs, but a similar fraction from animal half cytoplasm had no ability to form PGCs. The ‘PGC-forming activity’ demonstrated in the crude homogenate of the vegetal pole cytoplasm was not abolished by dialysis, lyophilization and heating to 90 °C for 10 min. When the homogenate was fractionated by differential centrifugation in 0·25 M sucrose, the ‘PGC-forming activity’ was recovered mainly in the precipitate of 15000g for 30 min. The precipitate of 7000 g for 10 min had also a little ‘activity’. The possibility was discussed that the ‘PGC-forming activity’ demonstrated in the vegetal pole cytoplasm was associated with the germinal granules in the germ plasm rather than the mitochondria.

The effect of egg rotation on the differentiation of primordial germ cells in Xenopus laevis

Development ◽  
1985 ◽  
Vol 90 (1) ◽  
pp. 79-99
Author(s):  
J. H. Cleine ◽  
K. E. Dixon
Keyword(s):  
Xenopus Laevis ◽  
Germ Cells ◽  
Germ Plasm ◽  
Primordial Germ Cells ◽  
Intermediate Zone ◽  
Gastrula Stage ◽  
Tail Bud ◽  
Axis Orientation ◽  
Early Gastrula ◽  
Number Of Cells

Eggs of X. laevis were rotated (sperm entrance point downwards) either through 90° (1×90 embryos) or 180° in two 90° steps (2×90 embryos) at approximately 25–30 min postfertilization after cooling to 13°C. The embryos were kept in their off-axis orientation and cooled until the early gastrula stage. Rotation resulted in relocation of egg constituents with slight changes in the distribution of outer cortical and subcortical components and major changes in inner constituents where the heavy yolk and cytoplasm appeared to reorient as a single coherent unit to maintain their relative positions with respect to gravity. Development of rotated embryos was such that regions of the egg which normally give rise to posterior structures instead developed into anterior structures and vice versa. Germ plasm was displaced in the vegetal-dorsal-animal direction (the direction of rotation) and was segregated into dorsal micromeres and intermediate zone cells in 2×90 embryos and dorsal macromeres and intermediate zone cells in 1×90 embryos. In consequence, at the gastrula stage, cells containing germ plasm were situated closer to the dorsal lip of the blastopore after rotation — in 2×90 gastrulas around and generally above the dorsal lip. Hence, in rotated embryos, the cells containing germ plasm were invaginated earlier during gastrulation and therefore were carried further anteriorly in the endoderm to a mean position anterior to the midpoint of the endoderm. The number of cells containing germ plasm in rotated embryos was not significantly different from that in controls at all stages up to and including tail bud (stage 25). However at stages 46, 48 and 49 the number of primordial germ cells was reduced in 1×90 embryos in one experiment of three and in 2×90 embryos in all experiments. We tested the hypothesis that the decreased number of primordial germ cells in the genital ridges was due to the inability of cells to migrate to the genital ridges from their ectopic location in the endoderm. When anterior endoderm was grafted into posterior endodermal regions the number of primordial germ cells increased slightly or not at all suggesting that the anterior displacement of the cells containing germ plasm was not the only factor responsible for the decreased number of primordial germ cells in rotated embryos. Other possible explanations are discussed.

The positional effect of presumptive primordial germ cells (pPGCs) on their differentiation into PGCs in Xenopus

Development ◽  
1988 ◽  
Vol 102 (3) ◽  
pp. 527-535
Author(s):  
K. Ikenishi ◽  
Y. Tsuzaki
Keyword(s):  
Germ Cells ◽  
Germ Plasm ◽  
Germ Line ◽  
Anterior Part ◽  
Primordial Germ Cells ◽  
Positional Effect ◽  
In Series

To determine whether the location of ‘germ plasm’-bearing cells [presumptive primordial germ cells (pPGCs)] is crucial for their differentiation into PGCs in Xenopus, [3H]thymidine-labelled pPGCs were implanted into the anterior or posterior halves of the endoderm in unlabelled host neurulae. Labelled PGCs in the genital ridges of experimental tadpoles were investigated by autoradiography. When the labelled pPGCs were implanted into posterior halves of the endoderm where host pPGCs are situated, 65 and 77% of the experimental tadpoles (designated as p-tadpoles) had the labelled PGCs in series I and II, respectively. When implanted into the anterior halves, 20 and 27% of the experimental tadpoles (a- tadpoles) had the labelled PGCs in series I and II, respectively. In p-tadpoles, the average numbers of labelled PGCs per tadpole were 8á7 in series I and 10 in series II, whereas they were 2á0 in a-tadpoles of both series. Both the proportion and the average number in p-tadpoles of both series were significantly different from those in a-tadpoles. In both series, labelled PGCs in p-tadpoles were found to be distributed throughout the genital ridges while those in a-tadpoles were localized only in the anterior part of the ridges. These facts indicate that the location of pPGCs in the endoderm affects their successful migration into the genital ridges, and that not only the presence of the germ plasm but also the proper location in endoderm are prerequisites to PGC differentiation of the germ line cells.

scholarly journals DEADSouth protein localizes to germ plasm and is required for the development of primordial germ cells in Xenopus laevis

Biology Open ◽  
2012 ◽  
Vol 2 (2) ◽  
pp. 191-199 ◽  
Author(s):  
T. Yamaguchi ◽  
A. Taguchi ◽  
K. Watanabe ◽  
H. Orii
Keyword(s):  
Xenopus Laevis ◽  
Germ Cells ◽  
Germ Plasm ◽  
Primordial Germ Cells

Quantitative studies of germ plasm and germ during early embryogenesis of Xenopus laevis

Development ◽  
1975 ◽  
Vol 33 (1) ◽  
pp. 57-74
Author(s):  
P. McD. Whitington ◽  
K. E. Dixon
Keyword(s):  
Germ Cells ◽  
Germ Plasm ◽  
Primordial Germ Cells ◽  
Early Embryogenesis ◽  
Daughter Cells ◽  
Quantitative Studies ◽  
Endodermal Cells ◽  
Early Gastrula ◽  
Number Of Cells ◽  
Direct Counts

The germ plasm in the egg is partitioned between the first four blastomeres by the first two cleavage planes. Although the blastomeres divide 10–11 times through the rest of cleavage, as shown by reduction in their size, the number of presumptive primordial germ cells (p.p. germ cells) does not increase significantly. During and as a result of the formation of the first two cleavage planes, the germ plasm aggregates together and moves towards and along the cleavage furrows. At subsequent mitoses, the germ plasm is localized at one of the poles of the spindle and hence is segregated to only one of the daughter cells, thus explaining how mitosis occurs without increase in the number of cells with germ plasm. Early in gastrulation, the germ plasm moves to a perinuclear position, therefore ensuring that as mitosis continues, both daughter cells receive germ plasm and the number of p.p. germ cells increases. Direct counts of the number of p.p. germ cells and measurements of their volume suggest that they divide twice between early gastrula and the stage at which they leave the endoderm. The p.p. germ cells behave similarly to the adjacent endodermal cells until they begin to migrate to the gonad, an event which may represent the first overt signs of differentiation. Measurements of the volume of germ plasm suggest that there is no change through cleavage. The general conclusion is drawn that during cleavage, the morphogenetic determinant germ plasm is segregated to a few cells by the normal processes of cleavage and that subsequently these cells undergo a small number of cloning divisions which are contemporaneous with the first signs of differentiation.

Replacement of posterior by anterior endoderm reduces sterility in embryos from inverted eggs of Xenopus laevis

Development ◽  
1986 ◽  
Vol 94 (1) ◽  
pp. 83-93
Author(s):  
J. H. Cleine
Keyword(s):  
Cell Differentiation ◽  
Xenopus Laevis ◽  
Germ Cell ◽  
Germ Cells ◽  
Germ Plasm ◽  
Primordial Germ Cells ◽  
Inverted Position ◽  
Control Series ◽  
Germ Cell Differentiation ◽  
Tailbud Stage

The genital ridges of Xenopus laevis tadpoles reared from eggs kept in an inverted position contain less than 40 % of the number of primordial germ cells (PGCs) of controls (Cleine & Dixon, 1985). It has been suggested that this reduction is caused by the germ cells' ectopic position in the anterior endoderm of larvae from inverted eggs, from where they may be unable to migrate into the genital ridges (Cleine & Dixon, 1985). This hypothesis is tested here by interchanging anterior and posterior endodermal grafts between pairs of inverted embryos at the early tailbud stage. Replacement of anterior by posterior endoderm has no effect but replacement of posterior by anterior endoderm increases the number of PGCs in the genital ridges and significantly reduces the proportion of sterile embryos. In a control series, in which the same type of grafting was done with normal embryos, replacement of posterior by anterior endoderm reduced the number of germ cells to almost zero, but replacement of anterior by posterior endoderm nearly doubled it. These findings are explained in terms of the distribution of the germ cells in the endoderm at the time of grafting. The results firstly show that the position of the germ cells is crucial to successful migration and secondly they support the notion that germ plasm has a determinative role during early germ cell differentiation.

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